Problem: $ A = \left[\begin{array}{rrr}2 & 1 & 0 \\ 0 & 2 & 0 \\ 2 & 1 & 2\end{array}\right]$ What is $ A^{-1}$ ?
Answer: $ = \left[\begin{array}{rrr}\frac{1}{2} & -\frac{1}{4} & 0 \\ 0 & \frac{1}{2} & 0 \\ -\frac{1}{2} & 0 & \frac{1}{2}\end{array}\right]$